In view of their exceptionally high hardness, excellent wear resistance, and thermal stability, diamond-silicon carbide (SiC) composites have been used in various industrial applications such as machining, grinding, drilling, and mining. Diamond-SiC composites have been prepared by a variety of methods that include chemical vapor deposition, high-pressure high temperature (HPHT) liquid phase sintering, and low vacuum liquid phase infiltration.
Most available diamond-SiC composites are composed of microcrystalline diamond held together by microcrystalline SiC. Despite their extraordinary hardness and wear resistance, these composites have relatively low fracture toughness (<6 MPa·m1/2), which limits their potential applications.
Fracture toughness of diamond-SiC composites has been improved by incorporating nanocrystalline diamond into the composites. It is believed that the nanocrystalline diamond and SiC hinder dislocation growth and microcrack propagation in the composite better than microcrystalline diamond and SiC do, which improves fracture toughness. Such a composite has been reported by E. A. Ekimov, A. G. Gavrilliuk, B. Palosz, S. Gierlotka, P. Dluzewski, E. Tatianin, Yu. Kluev, A. M. Naletov, and A. Presz in “High-Pressure, High-Temperature Synthesis of SiC-Diamond Nanocrystalline Ceramics,” Applied Physics Letters, vol. 77, no. 7, pp. 954-956). The composite was prepared by the liquid silicon infiltration of nanocrystalline diamond powder under HPHT conditions HPHT (7.7 GPa, 1700-2300 K). The composite displayed high fracture toughness (10 MPa·m1/2) but was not uniformly dense. It was only partially densified. The infiltration depth was only 1-2 millimeters (mm) because the pores closed very quickly during infiltration due to the “self-stop process”; as silicon infiltrates through the pores, it reacts rapidly with diamond to form a silicon carbide phase that seals the pores and prevents further infiltration. Alternative methods that are not limited by the self-stop process may be required to overcome problems relating to the self-stop process in order to provide uniformly dense composites with high fracture toughness. Such a method would also minimize graphitization of nanocrystalline diamond, which has also been a problem in the past.
Uniformly dense, diamond-SiC composites having high fracture toughness remain desirable.